WD Red or Seagate Constellation CS would be your 2 best choices I'd say. The Seagate runs at 7200rpm so it's technically the faster drive since the WD Red uses "Intellipower" similar to that of the WD Green.

They're both classified as "value enterprise" drives I'd say and both have 3yr warranties.

I personally have 4x 3TB WD Red's in my QNAP TS-469L NAS and they've been running perfectly fine without so much as a hiccup.